New Crumb Rubber Technology - a life cycle extender for Porous Asphalt

Tafadzwa MafumaMuch Asphalt

Bitumen Rubber

- Conventional bitumen rubber A-R1 used in South Africa since 1980s- Bitumen rubber is an excellent solution for pavement surfacings

- extends service life- self-healing- prevents reflective cracking- carbon-black in rubber crumbs shields against UV action

- reduces life cycle cost- Conventional bitumen rubber has big environmental footprint

- high handling temperatures- special blending units - limited shelf-life

- New technology developed to reduce environmental footprint: A-R2- same rubber crumbs as used for A-R1- warm-mix alternative with F-T wax

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Comparison of A-R2 to A-R1

Penetration grade bitumen

F-T wax modified bitumen

(adapted from SABITA TG1, 2015)

Effect of F-T wax on binder viscosity

3So

ften

ing

Poin

t, °C

time, hours

Conventional AR1

Conventional AR1

A-R 2 @

Softening point over time

A-R2 Test Methods and Evaluation

Bitumen Rubber Specifications (adapted from F.J Pretorius et al,2018 )

A-R1 A-R2 Blending Temperature 200oC 180oC

Mixing Temperature 175 - 180oC 140 - 150oCPaving Temperature Minimum 135oC Minimum 100oC

Shelf life 4 – 8 hours at 190 - 200oC 7 days at 150oC

Test method S-R1 A-R1 S-R2 A-R2 TG1 TG1 TG1 TG1

Softening Point (R&B) oC MB-17 55-65 55 – 65 65 – 80 65 – 80

Dynamic viscosity 190oC (dPa.s) MB-13 20-40 20-50 - -170oC (dPa.s) MB-13 - - 10-40 10-40

Compression recovery

5min

% MB-11

>70 >80 >70 >701 hour >70 >70 >70 >70

24 hours - - >40 >404 days >40 - - -

Resilience 25oC % MB-10 13-35 13-40 10-40 10-40

Flow 60oC mm MB-12 15-70 10-50 - -70oC mm MB-12 - - 10-40 10-40

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A-R2 Application - Porous Asphalt

- Ultra-Thin Porous Surfacing (UTPS)- paved thinner than typical porous asphalt - grading coarser than typical UTFC to accommodate rubber crumbs

- High interconnected voids in porous asphalt – need for - thick film-thickness for

- cohesion- reduction in rate of oxidation of binder

- viscous binder for thick film coating with no drain-down- Different binders assessed for durability of porous asphalt

- A-E2, homogenous elastomeric polymer modified binder- A-R1, conventional non-homogenous polymer modified binder- A-R2, warm-mix alternative to A-R1

- Durability indicators assessed - Schellenberg drain-down- Cantabro Abrasion Test

- unaged, aged and moisture damage induced5

A-R2 Application - Porous Asphalt

A-R1 A-R2 A-E2 (Lime) A-E2 (Fibre)

Coarse Aggregate Fraction (%) 74.2 74.2 75 74.8Fine Aggregate Fraction (%) 17 17 17.2 17.1Filler (%) 3.2 3.2 2.2 3.2Additives (%) - - 1.0 (lime) 0.3 (fibre)Binder Content (%) 5.6 5.6 4.6 4.6Binder content (%) 5.6 5.6 4.6 4.6Compaction temperature (oC) 145 115 145 145Average void content (%) 17.8 17.9 18.5 18.7Schellenberg drain test (%) 0.12 0.1 0.23 0.19Film thickness (µm) 12.74 12.74 10.33 10.27

Cantabro Abrasion mass loss (%)Unaged 2.6 4.8 16.6 20.9Aged 6.7 6.9 24 22.8Moisture induced damage 8.3 8.7 26.5 28.1

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- Bitumen Rubber porous asphalt best performance comparatively- A-R1 and A-R2 have similar performance- A-R2 binder of choice for durability and extras:

- no bitumen rubber blending unit establishment (terminal blend)- reduced handling temperatures

A-R2 paving - no fumes

A-R1 paving - fumes

A-R2 Application - Porous Asphalt

- N5 Harrismith – first application of A-R2 in porous asphalt- functional surfacing for rideability improvement- approximately 2200 tons of porous asphalt produced

- A-R2 terminal blend supplied Tosas, Wadeville- Asphalt production plant in Bloemfontein

- A-R2 blend stable over 405km haul- extended shelf life at remote site

- Asphalt production temperatures of 170oC due to long haulage in winter

- energy saving compared to A-R1- no fumes- worker-friendly

- Porous asphalt hauled 330km from Bloemfontein to Harrismith

- A-R2 low viscosity enabled paving at 120oC and - Compaction at 100oC - After a year of service, the mat still looks as fresh as

newly paved- in-service performance to be monitored over the life-span of

project for more insight7

A-R2 porous asphalt mat behind screedA-R2 porous asphalt mat compactable at 114oC

Conclusion and Recommendations

- A-R2 bitumen rubber performs as well as A-R1 binder, with added benefits- extended shelf-life - economic for remote sites/small volume projects- relatively lower handling temperatures

- less ageing of binder during productions/placement- energy savings- environmental benefit- healthier conditions for users

- In-service performance to be monitored over the life-span of A-R2 surfacings for more insight

- Monitor performance of other applications of A-R2 such as BRACS and chip-and-spray

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A-R2 Application - experience

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Thank you for your attention